The invention relates to a device for cleaning a needle for sampling a liquid from a closed flask and, more particularly for taking blood samples in a blood analysis apparatus, and the invention essentially relates to a cleaning mechanism associated with a member for guiding the sampling needle.
There exist automatic blood analysis apparatuses that enable parameters, such as the number of white blood corpuscles and red blood corpuscles, the amount of haemoglobin, etc., to be determined from a blood sample. For this purpose, blood samples have to be taken from a flask and then transferred to one or more small receptacles on the apparatus, where they are subjected to the appropriate measurements. To sample the blood from a flask closed by a bung, it is known to pierce the bung using a needle which then dips into the liquid, and of drawing in the desired amount of blood through the needle. This operation is also carried out both on flasks the closing bungs of which are at the top and on inverted flasks the bungs of which are on the lower portion. Suitable mechanisms are, of course, used to move either the needle or the flask in order to pierce the bung. To be able to sample a very precise quantity of blood and then distribute it to the measuring unit or units, it is necessary to use, in all cases, a sampling valve mounted on the sampling tube between the needle and the analyzers. This sampling valve, particularly for the very small amounts of blood that it is wished to sample, is a component that has to be meticulously designed and is thus costly and difficult to adjust. In addition, it has to undergo rinsing between each sampling operation, at the same time as the needle is rinsed out. The rinsing is, moreover, often carried out by passing the mobile needle through a fixed rinsing case, or again, by means of a rinsing case that slides over a fixed sampling needle, as described in FR A 2 606 885 in the name of the Applicant. The aforementioned sampling valve is a necessity on existing apparatus insofar as, in blood sample flasks, there is often a slight positive air pressure or a slight negative air pressure inside the flask in relation to ambient air. If one wished to dispense with the use of the sampling valve, and still be able to sample exactly the intended amount of blood, the flasks for sampling would always have to be under constant pressure conditions, which is far from being the case.
The Applicant has found a solution to this problem which enables dispensing with the use of this sampling valve and which, at the same time, facilitates the operation of rinsing the sampling needle.